1. Field of the Invention
This invention relates to a method for stopping the leaking of a resin around the deckle portion of an extruder in which the deckle mounted on a die device of the extruder is moved lengthwise of a slit to thereby vary the length of the slit and to adjust the width of a flat film, and which is used in melting, extruding, and forming a thermoplastic synthetic resin.
2. Description of the Prior Art
A flat die device used for, extruding, and forming a thermoplastic synthetic resin must be provided with a means for adjusting the length of a slit in order to easily vary the width of the extruded products such as films or sheets.
Heretofore, two means, an inner deckle and an outer deckle, have been used as the means for varying this length of the slit. One means, that is, the inner deckle is designed so that a deckle, such as a piano wire is inserted into a gap formed in a portion of the lands of the die, and by means of the resin pressure, the deckle is pressed against, and placed in intimate contact with the lands to interrupt the flow passage of molten resin, thus adjusting the width of the film. The other means, that is, the outer deckle, is designed so that a jig is pressed against and mounted with a clamping metal piece on the outer surface of the die slit, and a sealed portion within the jig interrupts the flow of resin, thus adjusting the width of the film.
However, these conventional means have various difficulties and are not sufficient to prevent a flow of resin. Namely, the inner deckle has the disadvantages that it tends not only to produce a resin leak which is heavier than that of the outer deckle due to an incomplete seal caused by a slight bend of the inner deckle which occurs during operation or the like but also the inner deckle itself is worn to a great extent, and that the operability in moving the deckle is not good due to the bend of the deckle. On the other hand, the outer deckle has the disadvantage that since it is mounted on the outlet of the slit, an air gap extending from the die slit to a cooling roll for cooling and solidifying the molten film unavoidably becomes longer. As a result of this, neck-in which is the difference between the slit length and the film width becomes greater to render the thickness between the opposite edges of the film thicker. Thus, films of a uniform thickness can not be obtained efficiently. In addition, using the two means as described above, it is necessary to periodically remove a resin which has leaked around the die slit because of an unavoidable occurrence of the resin leakage, and moreover, a jig or the like to receive the resin which has leaked must be provided because of an incomplete seal, and as the case may be, a winding of the resin which has leaked around the cooling roll or the like tends to give rise to difficulties such as a stoppage in the production of films.